| 总结: | Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na<sub>2/3</sub>Ni<sub>1/2</sub>Mn<sub>1/2</sub>O<sub>2</sub>, with two- and three-layer stacking through Al substitution and Al<sub>2</sub>O<sub>3</sub> treatment. Layered Na<sub>2/3</sub>Ni<sub>1/2</sub>Mn<sub>1/2</sub>O<sub>2</sub> oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al<sup>3+</sup> ions and keeping the amount of Mn ions in Na<sub>2/3</sub>Ni<sub>1/2−x</sub>Al<sub>x</sub>Mn<sub>1/2</sub>O<sub>2</sub> leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migration between layers occurring during oxide cycling was manipulated by oxide morphology. The best cycling stability is observed for Na<sub>2/3</sub>Ni<sub>0.42</sub>Al<sub>0.08</sub>Mn<sub>1/2</sub>O<sub>2</sub> having a column-like morphology of stacked plate-like particles along the common faces. The treatment of the layered oxides with Al<sub>2</sub>O<sub>3</sub> mitigates the Mn dissolution reaction during electrode cycling in the NaPF<sub>6</sub>-based electrolyte, thus contributing to a high cycling stability.
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